Hydrocephalus is a condition afflicting patients who are unable to regulate cerebrospinal fluid flow through their body's own natural pathways. Produced by the ventricular system, cerebrospinal fluid (CSF) is normally absorbed by the body's venous system. In a patient suffering from hydrocephalus, the cerebrospinal fluid is not absorbed in this manner, but instead accumulates in the ventricles of the patient's brain. If left untreated, the increasing volume of fluid elevates the patient's intracranial pressure and can lead to serious medical conditions such as subdural hematoma, compression of the brain tissue, and impaired blood flow.
The treatment of hydrocephalus has conventionally involved draining the excess fluid away from the ventricles and rerouting the cerebrospinal fluid to another area of the patient's body, such as the abdomen or vascular system. A drainage system, commonly referred to as a shunt, is often used to carry out the transfer of fluid. In order to install the shunt, typically a scalp incision is made and a small hole is drilled in the skull. A proximal, or ventricular, catheter is installed in the ventricular cavity of the patient's brain, while a distal, or drainage, catheter is installed in that portion of the patient's body where the excess fluid is to be reintroduced. To regulate the flow of cerebrospinal fluid and maintain the proper pressure in the ventricles, a pump or one-way control valve can be placed between the proximal and distal catheters. Such valves can comprise a ball-in-cone mechanism as illustrated and described in U.S. Pat. Nos. 3,886,948, 4,332,255, 4,387,715, 4,551,128, 4,595,390, 4,615,691, 4,772,257, and 5,928,182, all of which are hereby incorporated by reference. The valves can be configured with inlet and outlet ends extending at a 90 degree angle to one another, thereby enabling the ventricular and drainage catheters that attach to these ends to form a right angle when implanted. Alternatively, the valves can include inlet and outlet ends extending at 180 degrees to one another so as to form an in-line configuration when assembled with the ventricular and drainage catheters. When properly functioning, these shunt systems provide an effective manner of regulating CSF in hydrocephalus patients.
After implantation and use over extended periods of time, these shunt systems tend to malfunction due to shunt occlusion. Frequently, the blockage occurs within the ventricular catheter. The obstruction can result from a number of problems, such as clotting, bloody CSF, excess protein content in the CSF, inflammatory or ependymal cells, brain debris, infection, or by choroid plexus or brain parenchyma in-growth through the openings of the ventricular catheter. Another potential cause of ventricular catheter occlusion is a condition known as slit ventricle syndrome in which the ventricular cavity collapses, thus blocking the openings of the ventricular catheter. If left untreated, the occlusion of the ventricular catheter can slow down and even prevent the ability of the shunt valve to refill, thereby rendering the shunt system ineffective.
In the past, the remedy for a clogged proximal catheter was to surgically remove and replace the catheter, which involved the risk of damage to the brain tissue or hemorrhage. The current trend is to rehabilitate the catheter in place through less invasive means. This can be accomplished in a procedure generally known as shunt or ventricular catheter revision which involves reaming the clogged catheter in its implanted state until the blockage is removed to thereby reestablish CSF flow through the ventricular catheter. Many shunt valves, such as the ones described in U.S. Pat. Nos. 4,816,016 and 5,176,627, are provided with a domed silicone reservoir that enables access to the attached ventricular catheter so that the system can be flushed out for this very reason. The self-sealing silicone dome can be pierced with a small needle to gain entry to the attached catheter, without affecting the ability of the dome to re-seal after the needle has been withdrawn. In domed valves with right angle access, i.e., where the ventricular catheter extends at a 90 degree angle to the drainage catheter, a surgeon can gain entry to the clogged ventricular catheter percutaneously by inserting a rigid endoscopic instrument such as an endoscopic cutting tool or endoscopic electrode through the dome of the valve and straight down to the attached catheter. Thereafter, the obstruction can be cleared by cutting, cauterizing, or coagulating using the endoscopic instrument.
Where the shunt valve forms an in-line configuration with the ventricular catheter, a greater amount of manipulation is required to access the attached catheter. Rather than being able to enter the catheter by inserting the endoscope instrument straight down through the domed reservoir, the surgeon must enter the domed reservoir at an angle and then manipulate the endoscopic instrument once inside the shunt valve until the opening of the catheter is reached. This poses a unique set of problems when performing shunt or catheter revisions on in-line configured shunt valves. If the surgeon overshoots or undershoots the angle of entry, he may risk puncturing the soft side walls of the valve, which are typically formed from a soft plastic, and damaging the system. There is thus a need for a device that will direct the endoscopic instrument once it is inside a domed reservoir of an in-line shunt valve towards the attached ventricular catheter, while preventing inadvertent puncturing of the shunt valve by the instrument.